Soldering flux

ABSTRACT

A solder flux comprises rosin, an activator, an optional surfactant and the dimer of linoleic acid.

TECHNICAL FIELD

This invention relates to a soldering flux and more particularly, to anon-corrosive soldering flux.

BACKGROUND OF THE INVENTION

In soldering electronic components, circuits, equipment, etc., variouskinds of fluxes are used together with soldering material so as toimprove the efficiency of the soldering operation, to secure thesoldered connections and to improve the long-term reliability of theconnections. Conventionally, three kinds of fluxes are mainly used: (1)water soluble flux which is made from inorganic acids, organic acids,amine hydrohalides, etc., (2) natural rosin and (3) activated rosinhaving a halogenated compound, e.g., an amine hydrohalide, incorporatedwith natural rosin.

Various additives have been added to rosin to form an activated rosinflux. Keto acids, for example, levulinic acid, have been combined withrosin (see U.S. Pat. No. 2,361,867). Adipic acid has also been combinedwith rosin in the formation of a flux core. Also, it has heretofore beenknown to combine adipic acid and levulinic acid with rosin to form asolder flux.

Water-soluble flux is very useful in removing oxides from the metalsurface to be soldered. However, there are disadvantages in that thewater-soluble flux is apt to destroy metallic material and to leaveresidues which corrode the soldered parts after soldering. The corrosionimpairs the reliability of the soldered parts with respect to electricaland mechanical properties. This undesirable property of water-solubleflux can only be solved by using an extremely efficient flux residueremoval and cleaning process.

Natural rosin which is available under a name of WW rosin (water whiterosin) presents no problems with respect to corrosiveness, but isinferior as a soldering adjuvant.

Activated rosin has a stability similar to natural rosin and causeslittle corrosion at room temperature. Also, fully activated or liquidrosin activated (LRA) fluxes have a strong fluxing action at thesoldering temperature due to activators, such as an amine hydrochloride,which are typically present in high concentrations such as 1 to 10weight percent of the resultant flux. However, the fully activated rosinor LRA flux has disadvantages in that a corrosive gas is produced atsoldering temperature and can harm the surface of metals such as copper,brass, etc. Moreover, the residues of the activated rosin combine withmoisture and produce an acid which causes spontaneous corrosion similarto that produced by the water-soluble flux. Presently available fluxescontaining organic hydrohalides, in the form of neutral salts, e.g.,glutamic acid hydrochloride, either form corrosive metal halides atelevated temperature or the residues thereof combine with moisture atroom temperature to form a corrosive acid and thus are used withpossible deleterious effect for electrical soldering applications.

U.S. Pat. No. 2,898,255 reveals an activated rosin comprising amonocarboxylic acid, such as formic acid, combined with a dicarboxylicacid, such as glutamic acid. Such a flux, however, is too acidic andcorrosive for practical use in electronics soldering operations. Such aflux is typical of an LRA flux which is corrosive, as evidenced by thestandard copper mirror test outlined in the Electronics IndustriesAssociation Standard Number RS-402, for liquid rosin fluxes (approvedMar. 27, 1973).

A soldering flux which is superior in fluxing action and is free fromcorrosive action at room temperature as well as free from harmfulresidues is therefore desired. Such a flux is described in U.S. Pat. No.4,168,996, issued Sept. 25, 1979. While the fluxes described in thatpatent meet the objectives as set forth above providing very highsoldering efficiency, a specific problem of solder adherence to thedielectric has been encountered when this or other fluxes are used onspecific types of substrates. The problem is most often observed whenthe substrate surface is an incompletely cured epoxy or rubber-modifiedepoxy. This solder sticking can result in electrical shorts leaving thecircuits frequently beyond repair. I have now discovered a means ofmodifying the previously described solder formulation of U.S. Pat. No.4,168,996 which is incorporated herein by reference to essentiallyeliminate solder sticking while still retaining the beneficialcharacteristics of the prior formulation.

SUMMARY OF THE INVENTION

The present invention is directed to a soldering flux and a method ofsoldering using said flux. The novel solder flux which is anon-corrosive type flux, comprises a rosin mixture comprising (a) rosin,(b) an activator having at least one halogen atom and at least onedestabilizing functional group and (c) a dimer acid, e.g., the onederived from linoleic acid.

In the preferred embodiment, the rosin mixture also includes an acidsurfactant selected from (a') a polycarboxylic acid, (b') a hydroxylsubstituent of (a'), (c') a keto acid and (d') a mixture of any of theforegoing surfactants.

BRIEF DESCRIPTION OF THE DRAWINGS

The effect of soldering with a novel solder flux as compared to a priorart flux may be seen with reference to FIGS. 1 and 2 wherein FIG. 1 is aphotograph of a printed wiring board soldered with a prior art solderingformulation while FIG. 2 is a photograph of a similar printed wiringboard having been treated with the novel solder flux prior to soldering.

DETAILED DESCRIPTION

The present invention is based upon the discovery of a unique dimer acidmodified non-corrosive solder flux. The term "corrosive" used herein indescribing the solder flux means that the flux either (1) leaves anionic residue on a surface being treated therewith, which ionic residueis present in an amount sufficient to corrode the surface upon theapplication of electricity thereto, or (2) is acidic enough to corrodethe surface to which it is applied and which typically exhibits a pH ofits aqueous solution of less then 3. The term "dimer acid" which iscommonly used in the chemical industry represents dimerized linoleicacid available, e.g., from EMMERY Industries Inc. as EMPOL dimer acid invarious gradations.

The novel solder flux comprises a rosin mixture comprising rosin, anactivator and a dimer acid. For most applications, the flux furtherincludes an acid solder surfactant. More particularly, the rosin mixturecomprises about 50 to about 80 weight percent of rosin, about 1.0 toabout 15 weight percent of a nonionic activator, from 0 to about 25weight percent of surfactant and from about 2 to about 25 weight percentof dimer acid. The terms "weight percent" and "percent by weight" asused herein mean weight of a component per total weight of a flux"solids".

The particular rosin employed in the formulation may be a natural rosinsuch as water white rosin (WW rosin). Water white rosin is a well knownmaterial. Chemically, water white rosin is a mixture of severalcompounds. While the specific composition of the individual rosinutilized will vary depending upon a raw material source, water whiterosin can generally be typified as a mixture of isomeric diterpeneacids. The three major components are abietic acids, D-pimaric acid andL-pimaric acid. An "average" rosin will comprise up to 80-90 weightpercent abietic type acids, with the pimaric acids comprising 10-15weight percent. The designation "water white rosin" refers to a grade ofrosin determined by a conventional colorimetric method.

In addition to water white rosins, other rosins, such as hydrogenatedwood rosin, and disproportionated, dimerized wood or WW rosin, toll oilrosin etc., as is well known in the art, can be employed.

Combined with the rosin in the mixture is a suitable activator. Anactivator is a compound which cleans and prepares the surface to besoldered as by removing undesirable deposits, such as oxides. A suitableactivator is any organic compound which contains at least one halogenatom, e.g., Cl, Br, etc., and at least one destabilizing atomic group oratom which permits the compound to decompose at or slightly below thesoldering temperature employed, typically about 185° C. to 277° C. Sincethe halogen atom is electron withdrawing, the destabilizing group oratom should also be electron withdrawing thereby creating an instabilityin the compound due to the competing, i.e., opposed, electronwithdrawing properties of at least two atoms or groups. Some typicaldestabilizing groups include the carboxyl group, carbonyl group, thearomatic hydrocarbon group or aryl group, e.g., phenyl, naphthyl, benzylp-tolyl and the phenacyl group etc., and a second halogen atom, e.g, Cl,Br, etc.

The activator compound may comprise any organic compound having thefollowing chemical structure ##STR1## wherein R₁ is a halogen atom, R₂is a destabilizing group selected from (1) the carboxyl group, (2) thearyl group, e.g, the phenyl, naphthyl, phenanthryl group, etc., thealkaryl group, the aralkyl group, the aryloxy group, (3) the carbonylgroup, e.g., ##STR2## where R' is an alkyl radical, cycloalkyl radical,aryl radical, heterocyclic radical or the hydrogen atom, and (4) thehalogen atom, R₃ and R₄ are the same as R₁ or R₂ or comprise an organicgroup or radical selected from alkyl, cycloalkyl, alkoxy andheterocyclic radicals or the hydrogen atom.

Preferred suitable activators include halogenated mono and dibasic (monoor dicarboxylic) organic acids. The acid activators have at least onehalogen atom, e.g., Cl, Br, etc., preferably at the alpha position,i.e., at the carbon atom adjacent to the carboxyl group. Suitablehalogenated monobasic (carboxylic) acids are those having at least 12carbon atoms, e.g., 2-bromo-tetradecanoic acid, 2-bromo-octadecanoicacid, and typically comprise 12 to 18 carbon atoms. If the monobasicacid has less than 12 carbon atoms the resultant rosin flux may be tooacidic and/or corrosive for electronics use and it may volatilize fromthe rosin flux and be lost prior to reaching the soldering temperature,e.g., typically 185° C.-260° C.

Suitable halogenated dicarboxylic (dibasic) organic acids are thosehaving at least 4 carbon atoms, e.g., halogenated substituted succinic,adipic, pimellic acids, etc., e.g., 2,3-dibromosuccinic acid,2-bromosuccinic acid, 2,2-dibromo-adipic acid, etc., and typicallycomprise 4 to 10 carbon atoms. If the dibasic acid has less than 4carbon atoms, the resultant flux is too acidic and is corrosive.

The activator is present in the resultant rosin mixture in an amountsufficient to remove surface deposits such as oxides. The activator ispresent in an amount ranging from about 1 to about 15 weight percent ofthe resultant flux "solids" mixture. If the activator is present in anamount less than about 1 weight percent, the activator effect thereof isinsufficient. If the activator is present in an amount greater thanabout 15 weight percent, then residues of a rosin flux employing therosin mixture occurring after soldering, may become corrosive.

Of course, mixtures of various activators described above may beemployed for the solder flux.

Generally, combined with the rosin and the activator in the rosinmixture is a solder surfactant. By "solder surfactant" is meant acompound which is principally added to the solder flux to aid in thespreading of the molten solder upon subsequent application thereof. Thesolder surfactant is a compound which improves the solder wetting rateof a surface, i.e., the surfactant enables better and more uniformspreading of molten solder across the surface to be soldered. Suitablesurfactants include polybasic acids, e.g., polycarboxylic acids such asdicarboxylic and tricarboxylic acids. The dibasic acids typically have 4to 10 carbon atoms. Suitable tricarboxylic acids typically compriseacids having 6 to 7 carbon atoms.

Other suitable surfactants include hydroxyl substituted polybasic acids,i.e., the hydroxyl substituents of the polybasic acids described above.Some typically hydroxyl substituted acids include tartaric acid andcitric acid, however, these acids are generally too acidic to be used inmanufacturing of sensitive electronic products.

In addition, keto fatty acids or ketone acids, e.g., levulinic ##STR3##are suitable surfactants. A particularly effective solder flux is onecomprising a surfactant mixture of a polybasic carboxylic acid, e.g.,adipic acid, combined with a keto acid, e.g., levulinic acid.

For most applications the selected surfactant is present in the rosinmixture in an amount of at least 5 weight percent of the resultant fluxsolids rosin mixture. However, for certain military applications, inorder to meet specific military requirements the amount of surfactantmust be either substantially reduced or omitted completely.

An additional constituent in the improved solder formulation of thepresent invention is the dimer of linoleic acid, i.e., dimerized 10,12octadecanedienoic acid.

    CH.sub.3 (CH.sub.2).sub.4 CH═CH--CH═CH--(CH.sub.2).sub.8 COOH

The dimer acid should be present in the amount ranging from about 5 toabout 25 weight percent. The addition of this specific dimer to thesolder flux formulation has obviated a solder sticking problem ashereinafter discussed.

It may be noted at this point that certain types of printed wiringsubstrates exhibit a tendency to interact with a molten solder alloyduring regular mass soldering operations in such a way as to lead to anexcessive deposit of solder on the printed wiring board circuit linesand at times on the printed wiring board substrate itself. These solderdeposits which are generally granular or gritty in appearance are foundin forms which are commonly termed webs, foils, wisps and crosses. Theseforms can lead to unwanted shorting between closely spaced conductivelines on the printed circuit board. Their presence becomes especiallydetrimental in the modern, high density, fine line spacing printedcircuit boards. Referring to FIG. 1, there is shown a printed circuitboard wherein the soldering operation used a prior art formulationsimilar to the novel formulation disclosed herein but without a dimeracid included in the formulation. It can be seen in various places thatunwanted production of solder buildup or faults occur. For example, onecan observe such faults in the areas indicated by circles drawn in overthe actual photo of the affected circuit.

In comparison, FIG. 2 shows a similar circuit board soldered afteremploying a novel flux as described herein which includes the dimeracid. It can be seen that when the novel flux is employed whichincorporates the dimer acid, the solder faults previously observed areessentially eliminated. Thus, the novel formulation significantlyreduces solder defects, such as in wave soldering applications.

In one embodiment, the rosin mixture, is typically contained in asuitable vehicle, e.g., a solvent carrier, in the form of a liquid toform a liquid solder flux. The rosin mixtures described above may bedissolved in a suitable solvent in order to form the liquid solder flux.Such solvent vehicle includes any solvent which is chemically inert withthe rosin mixture constituents and in which the rosin mixture issolderable. Some suitable solvents include aliphatic alcohols, e.g.,methanol, ethanol, isopropanol, 2-butoxyethanol, amyl alcohols, etc.,alkanolamines, e.g., ethanolamine, diethanolamine, etc., chlorinatedhydrocarbons, e.g., perchloroethylene, trichlorethylene, etc. or themixture thereof, as the specifics of the intended fluxing processrequired. Where a non-flammable liquid solder flux is required, thesolvent employed is a non-flammable solvent such as a chlorinatedhydrocarbon, e.g., perchloroethylene, trichloroethylene, etc.

The rosin mixture is combined with the solvent and mixed, usingconventional techniques, to form a homogeneous solution. For ease indissolution, the solvent is vigorously agitated and/or maintained at anelevated temperature, e.g., 90°-100° F. for isopropyl alcohol, and uponcomplete dissolution is cooled to room temperature. Of course, properhealth and safety precautions in handling flux solvents need to beexercised.

The rosin mixture is present in the resultant liquid rosin flux in anamount sufficient to yield the desired fluxing action, which in turn isdependent upon the metal members to be joined and the degree of solderto be applied and the manner of applying it. Typically, the rosinmixture is present in the liquid rosin flux in an amount ranging fromabout 10 to 50 weight percent, e.g., 10 to 80 weight percent rosinmixture, remainder ethanol. Specific fluxing requirements may requireflux composition outside the above range which is intended only forgeneral purpose fluxing operation.

Additionally, the liquid rosin flux may contain a foaming expedient inthe form of a surface active foaming agent to improve the wetting of andto insure uniform flux deposition on hard to wet surfaces to besoldered. Suitable foaming agents include non-ionic surface activeagents. Among typical suitable foaming agents are those derived fromflurocarbons such as the "ZONYL" series manufactured by E. I. DuPont deNemours; the "FLUORAD" series manufactured by Minnesota Mining andManufacturing Company (3M Company), e.g., a perfluoropolyacrylate suchas FC-430; polyethyleneoxy non-ionic ethers such as the "Triton"products manufactured by Rohm & Haas Company, e.g., "Triton X-100,""Triton X-165"; and non-ionic surface agents based on the reactionbetween nonylphenol and glycidol such as surfactants 6G and 10Gmanufactured by the Olin Company. The amount of surface active agent isnot critical, the amount being sufficient to provide the degree ofwetting and uniformity thereof desired. Typically, the surface active orfoaming agent is present in an amount ranging from 0.01 to 0.1 weightpercent of the resultant liquid flux.

Alternatively, instead of employing a foaming agent as a foamingexpedient, as described above, a stabilizer solvent which stabilizesfoaming may be combined with the suitable vehicle, e.g., ethanol,isopropanol, etc. Such suitable foaming expedients, that is suitablestabilizer solvents, include alkanolamines, e.g., ethanolamine,diethanolamine, triethanolamine, etc. Where the solvent vehicle does notalready contain an alkanolamine, the alkanolamine is added thereto tofunction as the foaming expedient. Typically, the stabilizer solvent,e.g., ethanolamine, is present in an amount of about 0.1 to about 2percent by weight of the total weight of the resultant flux.

In operation of the metal surface of a first member and the metalsurface of a second metal surface, to be soldered and joined together,are treated with the liquid solder flux using any conventionaltechnique, e.g., dipping, spraying, brushing, rolling, foaming, wavefluxing, etc. The solvent of the flux is evaporated and at least one ofthe flux treated surfaces is then treated with molten solder, againusing any conventional technique, e.g., wave soldering, to form adesired solder deposit. The second metal surface is contacted to themolten solder deposit to link the surfaces and the solder deposit iscooled below the liquidus temperature thereof to solder join thesurfaces together.

In wave soldering, for example, the liquid solder flux is pumpedcontinuously through a trough or other suitable vessel to form anexposed or standing wave of liquid flux or its foam. The metal surfaceof the first member and the second member is passed through or contactedwith the standing wave of liquid flux or foam. Each member is thenheated to remove the volatile constituents of the flux. A continuousstream of solder is then typically pumped up into a spout forming a heador wave of solder through which at least one of the members is passed towet the metal surface thereof to be joined.

Where extremely difficult to solder surfaces are encountered, e.g.,copper-tin-nickel alloy surfaces, metal surface shaving a heavy tarnishor metal oxide layer, etc., LRA solder fluxes, as classified in theElectronics Industries Association (EIA) Standard Number RS-402(approved Mar. 27, 1973) [for liquid rosin fluxes], have heretofore beenemployed which contain large concentrations, e.g., 1 to 12 weightpercent of the resultant flux of organohydrohalides, such as glutamicacid hydrochloride or amine hydrohalides, such as diethylaminehydrochloride and cetyl trimethylammonium bromide. However, such LRAfluxes are too corrosive and too acidic for most electronicapplications. The above-described novel liquid flux comprising the novelrosin mixture, solvent and optionally foaming expedient, is successfullyemployed for such difficult to solder surfaces. Preferably, a secondaryactivator is added to the above-described rosin flux mixture andoptionally the foaming agent or stabilizer solvent, to form a mildlyactivated or LRMA liquid flux which achieves extremely successfulsoldering to such extremely difficult to solder surfaces without theaccompanying defects of high acidity and corrosiveness. The secondaryactivator comprises any chemically compatible organohydrohalide which iscapable of releasing a hydrogen halide or a halogen itself at theelevated temperature employed, that is at the soldering temperatures,e.g., 185°-260° C. Suitable secondary activators include glutamic acidhydrochloride, amine hydrohalides, e.g., diethylamine hydrochloride,ethoxyamine hydrochloride and substituted ammonium halides such as cetyltrimethylammonium bromide. The maximum amount of the secondary activatorcombined with the rosin mixture and present in the resultant liquid fluxis critical. The secondary activator, e.g., diethylamine hydrochloride,is combined with the rosin mixture in an amount ranging from about 0.17to about 0.28 weight percent of the resultant combined components. Ifthe amount of the secondary activator is greater than about 0.28 weightpercent of the combined rosin mixture and secondary activator, then theresultant flux is too corrosive, leading to residues which corrode thesoldered surfaces or parts after soldering and application of electricalpower thereto, thereby impairing the reliability thereof with respect toelectrical and mechanical properties. Of course, such a condition cannotbe tolerated for electronic soldering applications. If the secondaryactivator is kept within the above critical concentration range, theresultant liquid flux is an LRMA or mildly activated flux as describedin the aforementioned EIA Standard Number RS-402.

A particularly superior liquid flux is obtained when the activatorcomprises a dibromostyrene, e.g., 1,2-dibromo-1-phenylethane, and thesecondary activator comprises diethylamine hydrochloride.

It is, of course, to be understood that the rosin mixture may becombined with any suitable vehicle known in the soldering art to formany conventional fluxing medium, e.g., solid, liquid, paste or paint,and the invention contained herein is not limited by the particularrosin mixture employed or the resultant flux medium itself, be it solid,liquid or paste.

In forming a solid or semisolid (paste) flux, the rosin mixture ofrosin, activator and surfactant (optionally combined with the secondaryactivator) is combined with a conventional binder material vehicle,e.g., a grease binder, a wax binder, a glue binder, paraffin wax, etc.,and additionally where a paste is desired, with a suitable solvent,e.g., a terpene, an alcohol, etc., which gives the proper consistency.Typically, a rosin mixture, comprising 0.3 to 7 weight percentactivator, at least one weight percent surfactant, 2 to 25 weightpercent dimer acid and typically 1 to about 15 weight percentsurfactant, and a remainder of rosin, e.g., 50 to 95 weight percentrosin, is present in an amount up to 50 to 95 weight percent in both thesolid flux and the paste flux, respectively.

In another embodiment, the rosin mixture of rosin, activator, dimer acidand surfactant, optionally combined with the secondary activator, isdirectly combined with the particular solder alloy to be employed in asimultaneous flux and alloy application. In one such application, therosin mixture is directly combined with the selected alloy in the formof a soldering paste. The solder alloy, which is in powder form, isintimately mixed or suspended in a medium comprising the rosin mixture(rosin, activator and surfactant), and a suitable paste carrier, such asfor example paraffin wax, turpentine, glycol ethers and/or polyethyleneglycols, etc. It is to be noted that any conventional paste carrierknown in the art may be employed provided that it is chemicallycompatible with the rosin mixture and the solder alloy selected.Typically, the powdered solder alloy is present in the paste in anamount ranging from 70 to 90 weight percent whereas the rosin mixture,comprising 50 to 96 weight percent rosin, 0.3 to 7 weight percentactivator, 1 to 25 weight percent dimer acid and a remainder of at leastone weight percent surfactant, 1 to about 15 weight percent surfactant,is present in an amount of 10 to 30 weight percent. The resultantsolder-flux paste may be applied to a surface to be joined by dispensing(syringe type), rolling, screening or stenciling.

In a second application for simultaneously applying flux and solder, therosin flux mixture (rosin, dimer acid, activator and surfactant) andoptionally the secondary activator is combined with a selected softsolder alloy, in the form of a solder core. The rosin mixture iscontained as a solid, powder or even as a paste, within a wire of thesolder alloy, functioning therein as the core. Usually, the solder alloyis simultaneously extruded with the flux mixture to form a solder core.Typically, the flux mixture, e.g., comprising 50 to 96 weight percentrosin, 0.3 to 7 weight percent activator, 1 to 10 weight percent dimeracid and a remainder of at least one weight percent surfactant, e.g., 1to about 15 weight percent surfactant, is present in the solder wire inan amount of about 0.5 to 5 weight percent of the total solder corewire. Dimer acid itself plays a role of the flux plasticizing agentneeded for the cored wire extrusion pocess.

It is to be pointed out and stressed hereat that the use of the rosinmixture comprising rosin, activator, surfactant and optionally thefoaming expedient and/or optionally the secondary activatorleads to asolder joint containing a minimum amount of solder as exhibited byforming a shallow solder joint meniscus.

EXAMPLE I

A. For comparison purposes, a printed wiring board comprising an FR4epoxy substrate with a copper pattern thereon was employed. The copperpattern had a solder coat thereon. A solder flux without a dimer acidwas prepared containing 23.0 weight percent WW Rosin, 3.0 weight percentazelaic acid, 0.6 weight percent styrene dibromide and 73.4 weightpercent isopropyl alcohol. The solder flux was applied, by brushing, tothe solder coated copper pattern. The solvent from the solder wasallowed to evaporate and the flux-treated copper pattern was immersed ina molten solder bath for 5 seconds. A dull finish, containing extraneoussolder deposits resulted as illustrated in FIG. 1.

B. The procedure of EXAMPLE 1-A was repeated except that 10 weightpercent of linoleic acid dimer was included in the rosin mixtureemployed in preparing the flux. The linoleic acid dimer was substitutedfor the equivalent amount of rosin in the flux mixture. As can be shownin FIG. 2, essentially all the extraneous solder deposits wereeliminated.

As previously indicated, the particular solder flux formulation dependson the mode of application of the solder, e.g., foaming or sprayapplication, brushing or dipping, as well as the means employed forsoldering, e.g., wave soldering, solder leveling, etc. Typical for wavesoldering employing foaming or spray application, the percent solids inthe solder flux is preferably from 15 to 40 percent. Other types of fluxused in applications, as stated, may require different solids content. Apreferred solder formulation in a liquid solder flux contains, by weightpercent, 8.5 percent linoleic acid dimer, 11.5 percent rosin, 1.5percent azelaic acid, 0.6 percent styrene dibromide and the balancebeing the vehicle, 77.9 percent isopropyl alcohol. Such fluxes arecapable of passing high reliability testing for such parameters asinsulation resistance, corrosion to copper, acidity and a halide test.In the event such high reliability testing is not required or if outsideindustry is desirous of using formulations for military equipmentemploying a rosin mildly activated (RMA) type flux, the amount of acidtype surfactant azeleic acid may be reduced or completely eliminatedfrom the formulation. Further for other mil specs it is preferable tosubstitute an aminehydrochloride for the styrene dibromide activator.

It is to be understood that the above-described embodiments are simplyillustrative of the principles of the invention. Various othermodifications and changes may be made by those skilled in the art whichwill embody the principles of the invention and fall within the spiritand scope thereof.

What is claimed is:
 1. A solder flux which comprises:(a) rosin; (b) anactivator having at least one halogen atom and at least onedestabilizing substituent; (c) a surfactant selected from the groupconsisting of (a') a polycarboxylic acid, (b') a hydroxyl substituent of(a'), (c') a keto acid and (d') a mixture of any of the foregoingsurfactants; and (d) the dimer of linoleic acid, wherein said activatoris present in an amount of from 1 to 15 weight percent and saidsurfactant is present in an amount of from 0 to 25 weight percent. 2.The flux as defined in claim 1 which further comprises a flux vehicle.3. The flux as defined in claim 1 which further comprises a secondaryactivator comprising an organohydrohalide.
 4. The flux as defined inclaim 1 which further comprises a foaming expedient selected from thegroup of expedients consisting of a surface active agent and astabilizer solvent.
 5. The flux as defined in claim 1 wherein saidactivator comprises a halogen substituted carboxylic acid.
 6. The fluxas defined in claim 1 wherein said surfactant comprises a polycarboxylicacid selected from the group consisting of dicarboxylic acid having atleast 4 carbon atoms, a tricarboxylic acid having 6 to 7 carbon atomsand a mixture thereof.
 7. The flux as defined in claim 1 which comprisesrosin, a dibromosuccinic acid and adipic acid.
 8. The flux as defined inclaim 7 which further comprises levulinic acid.
 9. The flux as definedin claim 1 which comprises rosin, azelaic acid and a dibromostyreneactivator.
 10. The flux as defined in claim 9 which further comprises asecondary activator comprising diethylamine hydrochloride.
 11. The fluxas defined in claim 1 wherein said rosin is present in an amount rangingfrom about 10 to about 80 weight percent, said activator is present inan amount ranging from about 1 to about 15 weight percent, said dimer ispresent in an amount of from 2 to 25 weight percent and said surfactantis present in a remainder amount of at least one weight percent.
 12. Theflux as defined in claim 11 wherein said rosin, said activator and saidsurfactant are dissolved in a solvent vehicle in an amount ranging fromabout 10 to about 80 weight percent of the resultant solution.
 13. Asoldering flux comprising a rosin mixture which comprises:(a) rosin; (b)an activator comprising an organic acid selected from the groupconsisting of a monocarboxylic acid having at least 12 carbon atoms, adicarboxylic acid having at least 4 carbon atoms and a mixture thereof,said organic acid having at least one halogen atom; (c) a surfactantcomprising an organic acid selected from the group consisting of (a') adicarboxylic acid having at least 4 carbon atoms, (b') a hydroxylsubstituent of (a'), (c') a keto acid and (d') a mixture of any of theforegoing acids; and (d) 2 to 25 weight percent of linoleic acid dimerand wherein said activator is present in an amount of from 0.3 to 7weight percent and said surfactant is present in an amount of 0 to 25weight percent.
 14. The flux as defined in claim 13 which furthercomprises a vehicle.
 15. The flux as defined in claim 14 wherein saidvehicle comprises a solvent selected from the group consisting of analiphatic alcohol, an alkanolamine, a chlorinated hydrocarbon and amixture of any of the foregoing solvents.
 16. The flux as defined inclaim 15 which further comprises a foaming expedient.
 17. The flux asdefined in claim 13 which further comprises a secondary activatorcomprising an organohydrohalide.
 18. The flux as defined in claim 13wherein said monocarboxylic acid activator comprises 12 to 18 carbonatoms.
 19. The flux as defined in claim 13 wherein said dicarboxylicacid activator, said dicarboxylic acid surfactant and said hydroxylsubstituent thereof each comprise 4 to 10 carbon atoms.
 20. The flux asdefined in claim 13 which comprises rosin, a dibromosuccinic acid andadipic acid.
 21. The flux as defined in claim 20 which further compriseslevulinic acid.
 22. The flux as defined in claim 13 wherein, in saidrosin mixture, said rosin is present in an amount ranging from about 50to about 96 weight percent, said activator is present in an amountranging from about 1 to about 7 weight percent, said dimer is present inan amount of from 2 to 25 weight percent and said surfactant is presentin a remainder amount of at least one weight percent.
 23. The flux asdefined in claim 22 which further comprises a secondary activatorcomprising an organohydrohalide combined with said rosin mixture in anamount ranging from 0.17 to about 0.28 weight percent of the totalweight of combined components.
 24. The flux as defined in claim 22 whichfurther comprises a solvent vehicle in which said rosin mixture isdissolved in an amount ranging from about 10 to about 80 weight percentof the resultant flux.
 25. The flux as defined in claim 24 which furthercomprises a foaming expedient.